UPDATE: Kiefer's Rep Speaks up!

“Kiefer worked with Freddie Prinze, Jr. more than 5 years ago, and this is the first he has heard of Freddie‘s grievances...Kiefer enjoyed working with Freddie and wishes him the best" says an unnamed Fox executive.

The Hollywood Reporter has the details...

Freddie Prinze Jr. had such an awful experience acting opposite Kiefer Sutherland in 24 that he "wanted to quit the business," he said.

"I went and worked for Vince McMahon at the WWE for Christ's sake, and it was a crazier job than working with Kiefer," Prinze told ABC News. "But at least he was cool and tall. I didn't have to take my shoes off to do scenes with him, which they made me do. Just put the guy on an apple box or don't hire me next time. You know I'm six feet and he's five four."

Prinze was at San Diego Comic-Con promoting his new Disney XD series Star Wars Rebels.

US Weekly tells us more...

"I did 24, it was terrible," Prinze Jr. said of his 2010 gig on the hit FOX television show. "I hated every moment of it."

"Kiefer was the most unprofessional dude in the world," the '90s heartthrob added about 24's leading man, now 47. "That's not me talking trash, I'd say it to his face, I think everyone that's worked with him has said that."

Sutherland's alleged lack of professionalism bothered Prinze Jr. so much that he considered giving up acting for a bit. "I just wanted to quit the business after that," he explained. "So, I just sort of stopped."